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Sydney Science Forum - Rewriting Himalayan History: Ancient oceans on the top of the world

By Katynna Gill

15 October 2012

Take a journey to the top of the world when Professor Jonathan Aitchison, Head of the School of Geosciences, presents his Sydney Science Forum: Rewriting Himalayan History on Wednesday 17 October.

Find out how his team's research is rewriting the history of how the Himalaya and Tibetan Plateau formed to become the world's largest elevated region, including the world's highest peak, Mount Everest.

Professor Jonathan Aitchison (left), Head of the School of Geosciences, presents his Sydney Science Forum: Rewriting Himalayan History on Wednesday 17 October. This photo shows him on a fieldwork expedition in the Ladakh Himalaya.

The Himalayan mountains are the classic example of what happens when two continents collide - geology textbooks will tell you that the Indian subcontinent collided with Eurasia 55 million years ago and produced the Himalayas.

However, new evidence collected and analysed by Professor Aitchison and his team indicate that the collision might have happened around 20 million years later - only 35 million years ago.

"We've spent the past 17 years working in the Himalaya and Tibet, looking at how this mountain range formed. It's a really important system to study as the massive mountain chain had a profound effect on global climate systems when it formed, diverting atmospheric circulation patterns and leading to the establishment of the Asian monsoonal weather pattern," said Professor Aitchison.

"As the highest landmass on Earth, the Himalayas still have a huge impact on our weather systems. So understanding how and when they formed is of fundamental importance as it affects our understanding of the rates of numerous global processes," explained Professor Aitchison.

He and his team have found that India experienced multiple collisions as it travelled north, with the final collision between India and Asia occurring considerably later than originally thought.

"We looked at a number of indicators to determine when the mountain range formed. Examining the youngest marine rocks that were deposited between India and Asia showed that the collision between these two land masses happened around 35 million years ago. Obviously, once India and Asia had collided there was no longer an ocean between them and therefore no new marine rocks, so looking at the last marine rocks in the area gives us an indication of when the area last had an ocean above it," said Professor Aitchison.

Professor Jonathan Aitchison's Geosciences Honours student Tom Harvey collecting rocks in Tibet in 2012. Hear how Professor Aitchison and his team are rewriting Himalayan history with their findings of how the Himalaya and Tibetan Plateau formed to become the world's largest elevated region.

"We also looked at the age of the youngest subduction-related volcanic rocks along the southern margin of Asia. Subduction is when one tectonic plate moves below another tectonic plate as they converge, typically resulting in volcanic activity, like what we see around the Pacific 'ring-of-fire'. Once the Tethys Ocean, which used to lie between the ancient continents of Gondwana and Laurasia, had disappeared as oceanic crust north of India subducted beneath Asia, there was no more volcanism of this type, so the youngest such rocks also give us an indication of timing."

To determine the timing of formation of the Himalaya and Tibetan Plateau the team also looked at the relative positions of India and Asia through time and regional geological patterns.

"Examining the appearance and nature of coarse-grained sedimentary rocks also helped us work out the timing. When tectonic plate collisions occur, pushing up mountain ranges, large amounts of coarse sediment are shed as gravels off the new mountain chain."

Find out how his findings are rewriting geological history, when Professor Aitchison presents the results from his research group's work, including that of some of his talented students over 16 years in Hong Kong and now at the University of Sydney.

"The Himalayas are the geologically modern laboratory that we use to understand processes that might have affected much older rocks, like the ancient eroded mountain chains in Australia. We use the Himalayan system as our modern day example to understand ancient mountain systems," said Professor Aitchison.

Professor Jonathan Aitchison and Dr Aileen Davis, a geologist who now teaches at Monte St Angelo Mercy College, standing in front of the north face of Mount Everest.

"Working in the Himalayas is brilliant. It is like a dream come true, with scenery on steroids! However, conditions can at times be a little difficult as we are working at altitudes up to 6000 metres above sea level. At 5300 metres, where we spent most of our last trip, the atmospheric pressure is about 500 millibars compared with 1000 millibars at sea level, which can make breathing a little more challenging. But it is a truly remarkable area to work in."

Join Professor Aitchison as he reveals his amazing geological discoveries, accompanied by breathtaking photos of the Himalayan scenery, taking us on a journey to the top of the world.

Sydney Science Forum - Rewriting Himalayan History: Ancient oceans on the top of the world